“I'm getting too old for this ghost-catching tomfoolery.”
—Professor Elvin Gadd, when he meets Luigi in Luigi's Mansion

Professor E. Gadd, full name Professor Elvin Gadd (sometimes Dr. E. Gadd; Japanese: オヤ・マー博士 Professor Oya Mā), is the main deuteragonist and the elderly doctor/scientist that first appears in Luigi's Mansion and is the real founder/owner of Gadd Science, Inc. He always speaks in ambiguous and weird gibberish (supplied by Kazumi Totaka, who took inspiration from Animal Crossing's "Animalese" when inventing the voice), but the translation is always provided in a text box.

Storyline

In Luigi's Mansion, Luigi enters the mansion's Parlor, and is saved from ghosts by a strange old man wielding a vacuum cleaner. Professor E. Gadd reveals he lives in a house near the mansion, where he researches his favorite subject: ghosts. Luigi explains his brother Mario is missing within the house, so the professor decides to help Luigi by giving him two of his inventions, the Poltergust 3000 and the Game Boy Horror. The professor continues to help Luigi throughout the game, giving him help and tips how to suck up these pesky ghosts by shining the torch on the ghost then using the Poltergust 3000 to suck up the ghost.

Luigi's Mansion 2

He also appeared in Luigi's Mansion 2, or Luigi's Mansion: Dark Moon, which was initially released on the Nintendo 3DS in late March of 2013.

Trivia

The doctor's name is a pun of the word "egad" which is a word of surprise.

Whenever the professor says Luigi in the textbook, he will always say Ruīji (The Japanese term for Luigi)